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Sex Determination Flashcards

Exam 2

1
Q

What happens if Sxl expression is overexpressed in XY? If it is lost in XX?

A

Overexpression: Males will develop female characteristics

Loss: Females will gain male characteristics…VERY LETHAL

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2
Q

XY Sex Specification (4 gene steps)

A

Sry –> Sox9 –> Dmrt1, Amh –> testis formation

NOTE: Sry does not need to be activated for a long time bc of Sox9

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3
Q

What is the genital ridge?

A

Thickening of tissue in an embryo that develops into the gonads, or sex organs

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4
Q

What are primordial germ cells (PGCs)

A

Gamete progenitor cells that ariseelsewhere and migrate into the developing gonads.

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5
Q

Where do PGCs originate in mammals?

A. In the ovaries or testes depending on whether the individual is a male or a female.

B. In a particular posterior region of the early embryo.

C. In a particular region of the posterior hindgut of the embryo.

D. Along the genital ridge.

A

B. In a particular posterior region of the early embryo.

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6
Q

What happens if there is a homozygote deletion of dsx in male and female flies?

A

loss of sexual feature in both sexes….AKA “blank state”

Note: getting something in between sexes that is not differentiated

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7
Q

What is alternative splicing?

A

Process that allows a single gene to produce multiple proteins by inducing or excluding certain exons in the mRNA

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8
Q

When does PGC migration occur? Week #…

A

6 weeks post-fertilization

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9
Q

In turtles, what happens if Dmrt1 is deleted? What if it is overexpressed?

A

Causes sex reversal

  • deletion: male to female
    -overexpression: female to male
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10
Q

Which gene in XY and XX are mutually exclusive? (ie.e inhibit each other)

A

XY - Sox9
XX - B-catenin

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11
Q

XX Sex specification

A

Wnt signaling stabilizes B catenin, leading to ovary formation.

BONUS: genes involved: Wnt4 and Rspo1

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12
Q

Define gynandromorph.

A

Animal has both male and female characteristic

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13
Q

Mechanism of dose compensation in worms in XX

A

X-linked transcription factors
┴ (inhibit)
Dosage compensation complex
↓ *(binds to chromatin and recruits Chromatin remodeling enzymes)
↓
Histone hypermethylation OR hypoacetylation
↓
Decreases gene expression

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14
Q

What is gametogenesis?

A

Formation of the gametes (germ cells) in the gonad

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15
Q

Describe temperature sex determination in Trachemys scripta (turtles): MPT (5)

A

No high levels of Ca2+ bc low temp
┴
pSTAT3
↓
Kdm6b
↓
Dmrt1
↓
Male gonad

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16
Q

Secondary Sex Determination: XX

Gonads, Germ cell location, Duct, Hormone secreted

A

Gonads: Ovaries
Germ cell Location: Inside follicles of ovarian cortex
Duct: Müllerian Duct

Hormone: Estrogen

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17
Q

Define sequential hermaphrodite + 2 conditions + example

A

When the animal changes their sex at some point –> may depend on size or social factors (absence of other sex)

Ex: clownfish

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18
Q

What are bipotential gonads?

A

Precursor tissue derived from the genital ridge inMammals, from which the male and female gonads diverge.

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19
Q

What are gametes?

A

Reproductive cell through which sexually reproducing parents pass chromosomes to their offspring

Egg or sperm

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20
Q

Explain the primary or gonadal sex determination in mammals (4 steps)

A
  1. Migration of PGCs to endoderm through hindgut
  2. Crossed the genital ridge into gonads
  3. Bipotential gonads begin to develop as either testes or ovaries depending on XX or XY chromosomes
  4. Based on those chromosomes, female or male phenotype is expressed.
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21
Q

What is fertilization?

A

Fusion of male and female gametes

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22
Q

Mechanism of dose compensation in fruit flies in XY

A

Msl genes
↓ (causes overexpression of x-linked genes)
X-linked transcription factors
┴ (inhibit)
Dosage compensation complex
↓ *(binds to chromatin and recruits Chromatin remodeling enzymes)
↓
Hyperacetylation
↓
Increases gene expression

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23
Q

Describe the genetic mechanism behind sex specification in chicken (ZZ and ZW)

A
  1. Males have 2 copies of Dmrt1 –> activates Sox9 –> activates Amh later on
  • One Dmrt1 –> activate testis pathway
  • Second Dmrt1 –> inhibit ovary pathway
  1. Loss copy of Dmrt1 in ZZ (males) = ZW (female)
    - One Dmrt1 –> activate testis pathway
    - No Second Dmrt1 –> activates ovary pathway, which inhibits testis pathway
24
Q

Describe sex determination in flies: XY

A

Late expression (Maintanence promotor): Exons 1-4 (3 has STOP codon)

Female-specific splicing factor (Tra)
↓ (No Slx= no binding)
Truncation bc of stop codon
↓
Dsx gene
↓ NO Female specific splicing factor)
Male Dsx protein

25
The Sxl gene in flies is only active in ____
females
26
What is the specific term for organisms that have some female and some male body regions? A. Androgen insensitive B. Gynandromorphs C. Estrogen insensitive D. Polyploid
B. Gynandromorphs
27
When do PGCs begin to diffirentiatate into female or male characteristics? Week #...
7 weeks post-fertilization
28
As PGCs move through the genital ridge, the expression of pluripotency genes _____
decreased; commitment to germ cell fate
29
Which statement is true of the doublesex (dsx) gene? A. It is expressed in all body cells of males and females. B. It is expressed in both male and female Drosophila, but only in cells that differ between the sexes. C. It is expressed only in the gonads. More than just gonads D. It is expressed only in the reproductive cells of hermaphrodite organisms. No in hermaphrodites
B. It is expressed in both male and female Drosophila, but only in cells that differ between the sexes.
30
What is Amh?
Anti-Müllerian hormone; Inhibit Müllerian duct formation, thus preventing formation of the uterus and oviducts.
31
Know 2 examples of environmental cues inducing sex determination.
1. Presence or absence of males in a species group (ex: komodo dragons) 2. temperature (ex: turtles)
32
What is androgen insensitivity syndrome?
Condition in which an XY individual has a **mutation in** the gene encoding the **receptor protein that binds testosterone**. - XX external phenotype - Lack of a uterus and ovaries - Presence of testes
33
Gynandromorph vs. Hermaphrodites
Gynandromorph → Both M/F characteristics Hermaphrodites → Both M/F sex organs
34
Compare gene dosage compensation in flies with nematode (ringworms)
Flies: **Increase in transcription** of X chromosome genes in XY Worms: **Decrease in transcription** X chromosomes genes in XX *By hypermethylation (reduces gene expression)*
35
Who is homogametic in mammals? Fruit flies? Birds?
Mammals: Female Fruit flies: Female Birds: Male
36
Describe temperature sex determination in Trachemys scripta (turtles): FPT (7)
temperature-sensitive calcium channel opens (bc high temps) ↓ Ca2+ intracellular increases ↓ phosphorylates STAT3 ┴ Kdm6b ┴ Dmrt1 ↓ Increases histone methylation ↓ female gonad
37
What is the role of pSTAT3?
It inhibits Kdm6b at high temperatures
38
Describe gene dosage compensation in mammals.
Dosage compensation of X-linked genes is achieved by repression of one of the two X chromosomes in female cells. - X- activation of one chromosome--> becomes a Barr body and prevents excess transcription of genes on that chromosome
39
In Trachemys turtles, what gene is expressed in function of the temperature in a way that makes it an important sex determinant? A. Dmrt1 B. Sxl C. Doublesex D. Sry
A. Dmrt1
40
Protandry vs Protogyny
**Protandry**: Male → Female **Protogyny**: Female →Male
41
What do Leydig cells do?
Release testosterone
42
Differences between mammal and bird sex specification (2)
- Dmrt1 is expressed before Sox9; mammals are the opposite NOTE: More important player than Sox9 (opposite in mammals)
43
What do follicle cells do?
Release estrogen
44
What is congenital adrenal hyperplasia?
Presence of excess testosterone results in female internal sex organs but external genitalia that may be ambiguous or masculinized.
45
Describe sex determination in flies: XX
Early expression (Establishment promotor): Exons 1,2,4 Female-specific splicing factor (Tra) ↓ *(Slx binds)* Functional female specific splicing factor protein ↓ Dsx gene ↓ *Female specific splicing factor)* Female Dsx protein
46
Secondary Sex Determination: XY Gonads, Germ cell location, Duct, Hormone secreted
**Gonads**: Testis **Germ cell Location**: Inside testis cords **Duct**: Wolffian Duct **Hormone**: Testosterone
47
High levels vs low levels of Kdm6b
High: Dmrt1 is not expressed as much Low: Dmrt1 is expressed
48
What is the function/ role of Kdm6b?
Regulates Dmrt1 expression as it is a histone demethylase
49
Do simultaneous hermaphrodites have sex chromosomes?
No; there is no need for a genetic mechanism to determine sex
50
Define simultaneous hermaphrodite + Example
Individuals have fully functional male and female reproductive organs at the same time Ex: snails
51
Where do PGCs originate in mammals?
The posterior region of the early embryo near the allantois
52
What do sertoli cells do?
Sertoli cells release Amh --> inhibits Müllerian formation
53
What happens if Sry is added to XX? If it is removed?
1. Will become XY 2. Will revert to XX
54
What is primary sex determination?
Determination of gonads (ovaries or testes) based on chromosomal sex
55
Which structure develops into the major components of the reproductive tract of female mammals (the oviducts, uterus, cervix, and upper vagina)? A. Sertoli cells B. The genital tubercle C. Mullerian ducts D. The Wolffian ducts
C. Mullerian ducts
56
What is secondary sex determination?
Formation of the other sexual characteristics induced by gonads directed by hormones

Developmental Biology (4 decks)

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